Dumpvalve - warning (it would seem!)
04 January 2002, 12:44 PM
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this is from MRT's website...
Few sales people will take the time to explain that am externally venting (as opposed to fully plumbed ) valve confuses the A/F meter, as a result the ECU has no idea that air has been vented and thus causes a huge change in fuel mixture ( as the ECU thinks there is more air than there really is) resulting in a very rich mixture. That's why the standard one's outlet is after the A/F meter. This end result is funny misfires and flat spots.
Plus you will consume a lot more fuel
Most people argue that why then are they available?! Because "most" people want the whoosh noise, its as simple as that! Market forces!
There are some excellent new multi venting BOV's that will give you the noise without the flat spots, refer the MRT on line shop for details and pictures
Few sales people will take the time to explain that am externally venting (as opposed to fully plumbed ) valve confuses the A/F meter, as a result the ECU has no idea that air has been vented and thus causes a huge change in fuel mixture ( as the ECU thinks there is more air than there really is) resulting in a very rich mixture. That's why the standard one's outlet is after the A/F meter. This end result is funny misfires and flat spots.
Plus you will consume a lot more fuel
Most people argue that why then are they available?! Because "most" people want the whoosh noise, its as simple as that! Market forces!
There are some excellent new multi venting BOV's that will give you the noise without the flat spots, refer the MRT on line shop for details and pictures
04 January 2002, 01:36 PM
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Matt,
I have had an HKS unit fitted to my car which is Vent to Atmosphere... I too am wondering whether it is responsible for the occasional flatspot and fierce fuel consumption I am getting (or not as the case may be!). When I raised this with the guys who fitted it, I was assured it would not cause any problems and I fully trust their very valued opinion.
However, this is the not the first time I have read about problems with V to A dump valves. Any other advice/ opinions anyone??
Kev
I have had an HKS unit fitted to my car which is Vent to Atmosphere... I too am wondering whether it is responsible for the occasional flatspot and fierce fuel consumption I am getting (or not as the case may be!). When I raised this with the guys who fitted it, I was assured it would not cause any problems and I fully trust their very valued opinion.
However, this is the not the first time I have read about problems with V to A dump valves. Any other advice/ opinions anyone??
Kev
04 January 2002, 01:40 PM
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Mattski, that's exactly as I understood it which is why I've always thought that on a OEM ECU, they are a waste of time.....(unless you *really* want the noise 
)
Matt
)Matt
04 January 2002, 01:44 PM
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indeed...
I think if you are going to replace the dumpvalve get a recirculating one (i.e. the ECU will still have a grasp of things then!). I would tend to trust MRT, I don't think they would say it for no reason.
On my MY94 WRX I put a bailey atmos dumpvalve on it and that too developed flat-spots and fuel consumption went up... I didn't like it in the end so took it off and sold it. (noise also got annoying)
ta,
Matt
I think if you are going to replace the dumpvalve get a recirculating one (i.e. the ECU will still have a grasp of things then!). I would tend to trust MRT, I don't think they would say it for no reason.
On my MY94 WRX I put a bailey atmos dumpvalve on it and that too developed flat-spots and fuel consumption went up... I didn't like it in the end so took it off and sold it. (noise also got annoying)
ta,
Matt
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04 January 2002, 05:03 PM
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I've got the Scoobysport dumpvalve (Forge, i think) and have had no problems at all.
As for noise, i don't think its that noisey, or i'm just a boyracer
it only makes noise when you go from full throttle to lift-off
If it does make it run richer would'nt this only be on lift-off when it vents to atmosphere. Plus this is good for flames
Scott
As for noise, i don't think its that noisey, or i'm just a boyracer
it only makes noise when you go from full throttle to lift-offIf it does make it run richer would'nt this only be on lift-off when it vents to atmosphere. Plus this is good for flames
Scott
04 January 2002, 05:40 PM
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This has been covered, erm, quite a few times, but since search is not working, I'll give my balanced & diplomatic opinion again...
Dumpvalves are utter crap. Period.
Vent to atmo's are the worst: your closed loop ECU control will suffer. Period.
Recirculating aftermarket ones : don't bother unless you intend to run boost > 1.4 bar if you have a MY99/00, on earlier models there are known problems with dumpvalves, replace with MY99 item in that case.
Personally in this weather I see up to 1.4 bar on my VF23, and not a glitch from the standard plain Subaru item.
Worst thing is that the aftermarket junk often fails to close again after a while (grease gets diluted with oil that comes through the intercooler), so they start sucking in "false air", again messing up your fuel mixture. They also fail to open then, giving better throttle response (dump valves slow you down) but destroying the 270° bearing turbos.
The fact that you can buy them in anodized blue or red colors should tell you enough about their "motorsport" value
They guy that works on my car refuses to fit his performance kits on cars with a non standard BOV. He had too much **** with them.
Buy an MP3 player with the sound
Theo
Dumpvalves are utter crap. Period.
Vent to atmo's are the worst: your closed loop ECU control will suffer. Period.
Recirculating aftermarket ones : don't bother unless you intend to run boost > 1.4 bar if you have a MY99/00, on earlier models there are known problems with dumpvalves, replace with MY99 item in that case.
Personally in this weather I see up to 1.4 bar on my VF23, and not a glitch from the standard plain Subaru item.
Worst thing is that the aftermarket junk often fails to close again after a while (grease gets diluted with oil that comes through the intercooler), so they start sucking in "false air", again messing up your fuel mixture. They also fail to open then, giving better throttle response (dump valves slow you down) but destroying the 270° bearing turbos.
The fact that you can buy them in anodized blue or red colors should tell you enough about their "motorsport" value
They guy that works on my car refuses to fit his performance kits on cars with a non standard BOV. He had too much **** with them.
Buy an MP3 player with the sound
Theo
04 January 2002, 10:16 PM
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Like Piravlos, For over 17 months now, I too have the Blitz blow off valve on my MY00 and so far no problems. No hesitation or flat spots, no excessive fuel consumption, better throttle response and nice sound, and on light throttle lift off sometimes, I get a nice pop, but no power gains.
I pull it off once every 6 months, (piece of cake), take it apart, (piece of cake), and give it a clean with a rag and WD40, coz sometimes with moisture they can stick, which will cause uneven idle. If you use anything else than a rag, such as sand paper to clean, they will leak, coz you would be taking meat off the piston and the bore.
Only for the people that like the sound. Nothing more really. Oh just slighty better throttle response.
Cheers
Wrexy.
I pull it off once every 6 months, (piece of cake), take it apart, (piece of cake), and give it a clean with a rag and WD40, coz sometimes with moisture they can stick, which will cause uneven idle. If you use anything else than a rag, such as sand paper to clean, they will leak, coz you would be taking meat off the piston and the bore.
Only for the people that like the sound. Nothing more really. Oh just slighty better throttle response.
Cheers
Wrexy.
06 January 2002, 12:32 AM
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When buying an externally venting type dump valve for an Impreza you need to ensure that you get the correct type.
The better (read more expensive) valves, such as the Blitz, incorporate a stronger spring to hold the valve shut at cruising speed when there is a moderate boost differential across the throttle butterfly.
This stops the loss of measured air flow and consequent mixture enriching which occurs with "cheapo" valves as they open partially.
The only time a properly engineered dump valve should open is when the throttle is snapped shut at high boost and there is a high differential pressure across the throttle. Under these conditions there is no effect on combustion.
I must agree with the previous comments however, It's just not necessary below 1.5 bar boost.
The better (read more expensive) valves, such as the Blitz, incorporate a stronger spring to hold the valve shut at cruising speed when there is a moderate boost differential across the throttle butterfly.
This stops the loss of measured air flow and consequent mixture enriching which occurs with "cheapo" valves as they open partially.
The only time a properly engineered dump valve should open is when the throttle is snapped shut at high boost and there is a high differential pressure across the throttle. Under these conditions there is no effect on combustion.
I must agree with the previous comments however, It's just not necessary below 1.5 bar boost.
07 January 2002, 02:41 PM
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I have got one on mine it was on the car when i bought it, i dont know what type it is and know virtually nothing about them.
When i am on the motorway mine seems to be releasing air while i am cruising at a constant speed, i have to keep pressing the accelerator further stop it. Is this normal?
Thanks
07 January 2002, 03:56 PM
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This is only for MY99 and before.
Stick with the OEM blow-off valve, just turn it around, inlet to outlet, this will give you better response plus you will be able to run over 1.2 bar.
The logic’s is very simple, the air pressure opens the valve so the valve is always open, when inverted the air pressure will keep the valve shut and only will open by the vacuum line.
It takes only a few minutes to do it plus is free
Regards
Stick with the OEM blow-off valve, just turn it around, inlet to outlet, this will give you better response plus you will be able to run over 1.2 bar.
The logic’s is very simple, the air pressure opens the valve so the valve is always open, when inverted the air pressure will keep the valve shut and only will open by the vacuum line.
It takes only a few minutes to do it plus is free
Regards
07 January 2002, 04:42 PM
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I have a MY96 with OE dump valve..
so you recon I should just swap inlet and outlet around?
Don't see how that would work.. please explain further...
My thoughts :
The valve is shut all the time and then when you lift off it opens allowing the air to re-circulate or escape to atmosphere (with the pssstttttt noise). Unlike what you say "the air pressure opens the valve so the valve is always open" but then maybe the Subaru item is different to normal blow off valve?
At the end of the day it is only taking the load off the bearing in the turbo when you shut the throttle as all that air pressure has to go somewhere... previous turbo car (MR2) came with a HKS, I bought the OE and fitted it as the HKS couldn't handle what I increased the boost to.. and the OE was better all round and could take the extra boost...
No one turned around wondering what on earth the "Pppppptttttsssstt" was anymore though... but then you get bored with that after a while,.... or at least I did.
Cell - They shouldn't leak like that, either it is faulty or a really cheap one... personally I'd put a wanted post in the wanted forum for an OE secondhand one... just my opinon mind...
ho ho JGM
so you recon I should just swap inlet and outlet around?
Don't see how that would work.. please explain further...
My thoughts :
The valve is shut all the time and then when you lift off it opens allowing the air to re-circulate or escape to atmosphere (with the pssstttttt noise). Unlike what you say "the air pressure opens the valve so the valve is always open" but then maybe the Subaru item is different to normal blow off valve?
At the end of the day it is only taking the load off the bearing in the turbo when you shut the throttle as all that air pressure has to go somewhere... previous turbo car (MR2) came with a HKS, I bought the OE and fitted it as the HKS couldn't handle what I increased the boost to.. and the OE was better all round and could take the extra boost...
No one turned around wondering what on earth the "Pppppptttttsssstt" was anymore though... but then you get bored with that after a while,.... or at least I did.
Cell - They shouldn't leak like that, either it is faulty or a really cheap one... personally I'd put a wanted post in the wanted forum for an OE secondhand one... just my opinon mind...
ho ho JGM
07 January 2002, 05:02 PM
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JGM,
I think i have the original somewhere the bloke gave me it when i bought the car mine is also a 96 UK turbo, you reckon i would be better putting it back on?
The other thing i noticed was the pipe connecting to valve looks a bit perished, maybe its leaking from there?
I will loose my whoosh noise if i fit the standard one wont i?
I think i have the original somewhere the bloke gave me it when i bought the car mine is also a 96 UK turbo, you reckon i would be better putting it back on?
The other thing i noticed was the pipe connecting to valve looks a bit perished, maybe its leaking from there?
I will loose my whoosh noise if i fit the standard one wont i?
07 January 2002, 05:07 PM
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I haven't looked under the Subaru bonnet that much but it was a 10minutes job on an MR2... assuming it is accessable easily on the Scoob then it is easy to swap and swap back if you don't like.
May well be the pipe... I'd change it... you might be losing Turbo power from it.. def not run correctly anyway.
Yes you'd lose the pssssttttt noise with the standard.. although you could vent a standard one to atmos for the same noise but I am sure it would run like a dog then...
ho ho JGM
May well be the pipe... I'd change it... you might be losing Turbo power from it.. def not run correctly anyway.
Yes you'd lose the pssssttttt noise with the standard.. although you could vent a standard one to atmos for the same noise but I am sure it would run like a dog then...
ho ho JGM
07 January 2002, 05:27 PM
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The OEM blow off is installed so the valve in normally closed by a spring that is calibrated at 1.2 bar.
Then installed as factory the manifold air pressure acts against this spring, so when the boost start to build up this valve will open in proportion with the build up pressure.
When you invert the valve, the spring plus the air pressure, both will close the valve and the valve will only open when you close the throttle and vacuum is built up.
So you will never recirculate air through this valve to the engine.
Just you have to be very careful that this vacuum line is good otherwise you will have no air dump.
Since there is no modification at all, you don’t dump the air to the atmosphere.
Regards
Then installed as factory the manifold air pressure acts against this spring, so when the boost start to build up this valve will open in proportion with the build up pressure.
When you invert the valve, the spring plus the air pressure, both will close the valve and the valve will only open when you close the throttle and vacuum is built up.
So you will never recirculate air through this valve to the engine.
Just you have to be very careful that this vacuum line is good otherwise you will have no air dump.
Since there is no modification at all, you don’t dump the air to the atmosphere.
Regards
07 January 2002, 05:41 PM
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I think I am with you now...
Any ideas what boost a standard ECU NOT PPP would allow boost wise?
I think my last scoob was running 14.5psi peak which dropped to 14psi and was held at 14... if I remember correctly..
Haven't fitted a boost gauge to this one yet..
Might blow my turbo if I am not careful a she has 90000miles on the dial...
ho ho JGM
Any ideas what boost a standard ECU NOT PPP would allow boost wise?
I think my last scoob was running 14.5psi peak which dropped to 14psi and was held at 14... if I remember correctly..
Haven't fitted a boost gauge to this one yet..
Might blow my turbo if I am not careful a she has 90000miles on the dial...
ho ho JGM
07 January 2002, 06:09 PM
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I have a bleed valve in the garage at home...
I shall invest in a gauge and fit the bleed valve then I think.
Look at reversing the dump valve too...
On the MR2 the pipes were easy to trace but the Scoob is hard to see where pipes go etc.. anyone got a picture with key showing what pipe goes where etc.. on a MY96... where to fit gauge and where to fit bleed valve... I know it is asking a lot but it looks like a mass of pipes to me...
Your scoob must go like stink with that set up! if only I had the money...
ho ho JGM
I shall invest in a gauge and fit the bleed valve then I think.
Look at reversing the dump valve too...
On the MR2 the pipes were easy to trace but the Scoob is hard to see where pipes go etc.. anyone got a picture with key showing what pipe goes where etc.. on a MY96... where to fit gauge and where to fit bleed valve... I know it is asking a lot but it looks like a mass of pipes to me...
Your scoob must go like stink with that set up! if only I had the money...
ho ho JGM
07 January 2002, 10:24 PM
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14k miles, MY99 WRX, HKS SQV, no problems so far.
What I'm struggling to understand is how an atmospheric dump valve can give you poor fuel consumption. I may be missing the point but thought the fuel adjustment is governed by the MAF and O2 sensors.
I think there is some confusion on how the rich running comes about. It's not through extra fuel, it's through less measured air reaching the cylinders due to it being dumped to atmos. Surely the amount of fuel being used is the same regardless.
And yes I do get pops and bangs..
What I'm struggling to understand is how an atmospheric dump valve can give you poor fuel consumption. I may be missing the point but thought the fuel adjustment is governed by the MAF and O2 sensors.
I think there is some confusion on how the rich running comes about. It's not through extra fuel, it's through less measured air reaching the cylinders due to it being dumped to atmos. Surely the amount of fuel being used is the same regardless.
And yes I do get pops and bangs..
08 January 2002, 01:30 AM
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Have a look at the description of the GFB blow-off valve (under products>turbo>blow-off) for the MY01 WRX at:
http://www.vividracing.com
Part venting/part re-circ and claims to reduce turbo lag/re-spool on gear changes. This sounds ideal, as I find a noticable lag going fron 1st to 2nd under hard acceleration. From my point of view a "small" noise would be nice, power gain is not what I'm after but reducing lag certainly is. Sounds ideal but can it be true?
Whats everyones view on this? This product is also offered by MRTrally and Scoobymania I believe.
Cheers
http://www.vividracing.com
Part venting/part re-circ and claims to reduce turbo lag/re-spool on gear changes. This sounds ideal, as I find a noticable lag going fron 1st to 2nd under hard acceleration. From my point of view a "small" noise would be nice, power gain is not what I'm after but reducing lag certainly is. Sounds ideal but can it be true?
Whats everyones view on this? This product is also offered by MRTrally and Scoobymania I believe.
Cheers
08 January 2002, 08:07 AM
#23
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I presume Pob that because there is less air going to the cylinders there is less power produced at that point so you put your foot down more to go at the speed you want, therefore putting more fuel in.... I dunno, I always throught that it only blew off (pun intended) when you put took your foot off the gas, but then I guess when changing gear for example when you reapply the throttle there is less air in the cylinder than the ECU thinks there is and less power so you plant your foot harder.
I am just guessing...
If the dump to atmos helps the turbo spool up quicker it is going to use more fuel anyway so might be nothing to do with the rich mixture when dumped to atmos...
I don't know anything about that blow off valve but it might be a way to go if you really want the sound.. surely you will gain the same problems only smaller... slight rich mixture rather than very rich etc... you makes your choice and takes you chances..
ho ho JGM
I am just guessing...
If the dump to atmos helps the turbo spool up quicker it is going to use more fuel anyway so might be nothing to do with the rich mixture when dumped to atmos...
I don't know anything about that blow off valve but it might be a way to go if you really want the sound.. surely you will gain the same problems only smaller... slight rich mixture rather than very rich etc... you makes your choice and takes you chances..
ho ho JGM
08 January 2002, 08:21 AM
#24
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Apart from the loss in performance that you may or may not get from the mixture becoming rich as air is dumped to atmosphere, the increased fuel:air ratio in the cylinders could wash oil from the bores and dilute the oil in the engine case. This effect occurs if you run a car on the choke or make frequent short journeys. If you have a vent to atmosphere dump valve you could be getting these rich running periods much more frequently so although the effect is much more suble than that of a choke or cold start circuit over time it may increase engine wear ? Just a thought.
08 January 2002, 08:34 AM
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Oh yeah definitly not a good thing to richen the mixture...
Scoobies run pretty rich already as it is to try and stop det...
Hence you can get away with small tweeks without going lean on a UK car as far as I understand it...
Just a thought but if you up the boost and fit a dump to atmos then the increased richness of the mixture might help stop det...
Although the rich mixture would mostly be in the wrong place.. on lift off rather than on full chat..?
I do a lot of miles and wouldn't like to fit a dump to atmos to my scoob as I am likely to be the one that ends up footing the bill rather than the next owner. But then any performance mods increase wear and reduce engine life... other people might have found that they run fine for 1000s of miles anyway.
Scoobies run pretty rich already as it is to try and stop det...
Hence you can get away with small tweeks without going lean on a UK car as far as I understand it...
Just a thought but if you up the boost and fit a dump to atmos then the increased richness of the mixture might help stop det...
Although the rich mixture would mostly be in the wrong place.. on lift off rather than on full chat..?
I do a lot of miles and wouldn't like to fit a dump to atmos to my scoob as I am likely to be the one that ends up footing the bill rather than the next owner. But then any performance mods increase wear and reduce engine life... other people might have found that they run fine for 1000s of miles anyway.
11 January 2002, 03:37 PM
#26
Fitted a Forge or Forge style Atmospheric one last night.
Loads of Whoosh Tish...but also flat spots and uneven idle when pulling up to rest.
I put it down to the spring being too weak for the Subaru application. I could try stretching the spring or putting a stronger one in, but to be honest can't be bothered.
Just gonna take of and put the standard one back on........ just glad I picked it up for peanuts....
Loads of Whoosh Tish...but also flat spots and uneven idle when pulling up to rest.
I put it down to the spring being too weak for the Subaru application. I could try stretching the spring or putting a stronger one in, but to be honest can't be bothered.
Just gonna take of and put the standard one back on........ just glad I picked it up for peanuts....
14 January 2002, 01:07 PM
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My car went in last week to have a service done and the ECU was reset (four codes were present ). I know have error code 23 back on the ECU within three days of it being reset. Could this be due to the Dump Valve confusing the ECU????
). I know have error code 23 back on the ECU within three days of it being reset. Could this be due to the Dump Valve confusing the ECU????
14 January 2002, 03:15 PM
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I don't know how significant it is, but I don't think anyone has discussed the potential downsides to the normal OEM re-circ dump valves...
When changing up gear (from full boost), the standard valve will go totally open. This results in the depressurisation of everything between the turbo and the throttle from around 1 bar back to around 0 bar (with respect to atmos)...
This means that the volume of this air will approximately double. All of this air (that does not go through the throttle) will start on a journey back out of the induction system, possibly being measured (as new air?) by the MAF? - I guess it can't measure direction?
This may also result in an additional increase in next-gear pickup, as the air must swing back into travelling in the other direction again.
Additionally, a well engineered dump valve should probably not simply open when the throttle is closed, but regulate the boost pressure to some nominal level, which would be a trade-off between compressor stall and giving some immediate pressure when the throttle re-opens.
Does anyone think any of these effects may be significant?
James
14 January 2002, 03:29 PM
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James, the recirc air enters the system again *after* the MAF, so it was already measured.
As for the power thing ... dumpvalves are only there to protect your turbo bearings. They cost performance, whichever type you put on.
As for the power thing ... dumpvalves are only there to protect your turbo bearings. They cost performance, whichever type you put on.